Development of vision

Monitoring the development and health of your child’s eye.

Our “vision system” works like taking a photograph with a camera, the eyes acting as our cameras and the brain acting as our developing house. When we are first born we don’t see very well.

During the first few years of life our brain learns to see and becomes more discriminating in its level of vision because it has processed more information. This is just like the way our knowledge base improves as we go to school, the more lessons we go to the more developed that part of our education.

As long as the eyes are sending good quality images, the brain will develop to its maximum ability. But if poor quality of images are sent, the level of development is limited. Think of the school analogy – if you only go to GCSE level lessons you can’t be expected to pass A level exams as you haven’t had sufficient input to develop with.

Development of vision has the same pattern. If poor images are sent to the brain (possibly because the eye is out of focus) then the brain’s visual system will only develop to that level at best. This is why it is important to try to compensate for any refractive (power) errors in the eye as young as possible so that a good quality image is offered to the brain to learn from.

The ability of the brain to ‘learn to see’ is best when very young and drops markedly as we age with little ability to improve once approximately eight years old, although some academics feel that some improvements can be achieved even in an adult eye.

Binocular Vision

When vision starts to develop, the brain will normally try to co-ordinate the two eyes together. As the discriminating ability of the vision improves so will the level of co-ordination. If something causes the vision to be poorer in one eye than the other then the incentive for the brain to co-ordinate the two eyes is lessened. Sometimes the brain no longer achieves the linking together of the eyes. Occasionally the vision in the two eyes can be very similar yet still the brain fails to link the eyes. The term we give this condition is “strabismus” but it is often described as a squint.

If the two eyes don’t co-ordinate, the brain receives two different images. For example if someone with a strabismus / squint looks directly at your nose with one eye the other eye will point to an area to the side, possibly an ear or even further away. This is obviously very confusing for the brain and it develops a mechanism to cope that involves ignoring some of the information sent to it from the errant eye, we call this “suppressing” the image. Think of it as a form of censorship of what the eye sees. This suppression generally only affects the central part of the vision (which is where we see clearest) and the brain still takes note of the peripheral part of the vision in the errant eye.

Amblyopic (or Lazy eye)

This hiccup to the normal development of vision unfortunately tends to become more deep set as time goes by. What now happens is that the good (fixating) eye is used fully by the brain and carries on with its development of vision. But as the errant (squinting) eye is now being partially ignored, it no longer keeps developing. It is as if the good eye still keeps attending classes and developing but the errant eye plays truant and stops its development. We then get a situation where one eye sees much better than the other and so there is even less incentive for the brain to try to work the two eyes together. The longer this carries on, the deeper the suppression becomes.

An eye where this arrested development takes place is called an “amblyopic” eye and is often referred to colloquially as a ‘lazy eye’.

To try to get over the problem we make sure that the best quality image possible is focussed on the back of the eye. Often this uses glasses to correct any power error in the eye, and hope that the brain starts using the better information to develop the visual system. As long as a strabismus with suppression has not started then this is often all that is needed to restart the development of vision.

If there is suppression already, it is necessary to make the brain use the poorer eye. Patching or covering the good eye, forcing the brain to use the poorer eye and develop its visual system, achieves this. Once the vision in the poorer eye has been improved we can offer the brain an incentive to co-ordinate the two eyes. Unfortunately sometimes even if the vision is brought up in the poorer eye the brain still doesn’t link the eyes together despite efforts and exercises given by the supporting optical team. It does seem that in some cases the trigger to link the two eyes is missing and cannot be developed.

If there is an amblyopic eye in a young child our first efforts are to improve the quality of image to try to maximise the development of the vision whilst that development is possible (when young). We then hope that with encouragement there will be development of binocular vision. Even if our ideal goal of binocular vision is not achieved there has still been a reward for the efforts made as the amblyopic eye will have developed as fully as it can and offers a safety net for the future as it would then be able to take over if the good eye was damaged or lost in an accident for example.

Most of the developmental aspects of vision have taken place by the age of approximately eight years old and so it is important to try to act as early as we can to achieve the best results. Unfortunately once this age his passed there is unlikely to be noticeable improvements in vision, as even though a corrected focus creates a better quality image being sent to the brain, the brain cannot fully use the better quality of information. An analogy would be that if I had studied to GCSE level Physics and was then given a book with Einstein’s Theory of Relativity in it I wouldn’t be able to understand it. All the information would be there but my brain would not be adequately developed to use / understand it. Unfortunately, unlike taking up studying when older, my visual development has reached a plateau at about eight years old and is unlikely to improve with exercises / training.

Many people with a ‘lazy eye’ worry that they think it is doing no work and so their good eye will be worn out early because it has to work harder. The ‘good’ eye is not working any harder than normal and it is just that the brain relies on it a little more than the poorer eye. There is absolutely no evidence of the good eye suffering in either the short or long term.

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